Boromir: one does not simply... walk into mortor...
Aragorn: its mordor
Boromir: what?
Aragorn: its "mordor", with a "d"
Boromir: one does not simply walk into mordor...
Frodo: um... yes you do...
Boromir: shut up!,no you dont!
Frodo: yes you do, you tottally do
Boromir: nuh-uh!. you need like... an army.
with, like... ninjas... and... um... wizards!
NINJA WIZARDS!
Gandalf: i'm a wizard!
Boromir: yeah, but you're not a ninja
maybe some bears, too... bears that shoot laser beams out of their eyes. oh man, that would be so frickin' AWESOME!

In J. R. R. Tolkien's fictional universe of Middle-earth, Mordor is the dwelling place of Sauron, in the southeast of Middle-earth to the East of Anduin, the great river. Frodo and Sam went there to destroy the One Ring. Mordor was unique because of the three enormous mountain ridges surrounding it, from the North, from the West and from the South, that protected this land from an unexpected invasion by any of the people living in those directions.

Mordor was a relic of the devastating works of Morgoth, apparently formed by massive volcanic eruptions. It was given the name Mordor already before Sauron settled there, because of its volcano Orodruin and its eruptions.

Mordor actually has two meanings: "The Black Land" in Tolkien's contrived language Sindarin, and "The Land of Shadow" in Quenya. The root mor ("dark", "black") also appears in Moria. Dor ("land") also appears in Gondor ("stone-land") and Doriath ("fenced land"). The Quenya word for Shadow is "mordo".

A proposed etymology out of the context of Middle-earth is Old English morthor, which means "mortal sin" or "murder". (The latter are descended from the former.) It is not uncommon for names in Tolkien's fiction to have relevant meanings in several languages, both those invented by Tolkien, and "real" ones, but this of course happens with any two languages. Mordor is also a name cited in some Nordic mythologies referring to a land where its citizens practise evil without knowing it, imposed on themselves by the society long created for that purpose. This quite fits with Tolkien's Mordor.